The Middle East respiratory syndrome virus (yellow) has infected at least 800 people globally and killed about a third of them.

AP

Originally published on June 5, 2014 2:40 pm

In the two years since Middle East respiratory syndrome was first diagnosed in people, scientists have struggled to figure out how we catch the deadly virus. Some blamed bats. Others pointed at camels.

Now scientists in Saudi Arabia offer the strongest evidence yet that the one-humped dromedaries can indeed spread the MERS virus — which has infected more than 800 people on four continents, including two men in the U.S.

Last October, a 44-year-old retired military man caught MERS while treating one of his drippy-nosed camels at a farm near Jeddah, scientists say. The camel was congested. The man applied something like a vapor rub directly to the camel's nose. A week later, he fell ill. He was admitted to an intensive care unit on November 3 and died on the 18th.

The MERS viruses isolated from both the man and camel had almost exactly the same the DNA sequence, scientists report Wednesday in the New England Journal of Medicine.

"It unequivocally demonstrates that transmission from camels to people is possible," says virologist Ian Lipkin from Columbia University, who wasn't involved in the study.

MERS causes pneumonia-like symptoms and sometimes organ failure. There's no cure or vaccine. So figuring out where the virus originates is key to stopping it.

Camels have been at the top of list. The MERS virus has been circulating in Arabian camels for more than two decades, scientists reported in February. And the virus has been found in a camels at a farm owned by two people who caught MERS in Qatar.

But these studies were missing one critical component, says immunologist Matthew Frieman of the University of Maryland: "The direction of the infection was never known," he says. Did the camels infect people or did people infect the camels?

The new study helps to answer that question.

The day the retired military man came to the hospital in Jeddah, infectious disease specialist Tariq Madani and his team at King Abdulaziz University in Jeddah looked for signs that the man's camel had caught MERS before him.

The team found the smoking gun: Antibodies appeared in the camel's blood before they were seen in the man's blood.

"The timing of the infections works with the idea that the camel directly infected [the owner]," Frieman says. And not vice versa.

The findings are important, Frieman says, because they may help convince people to take precautions when handling camels. "There's a lot of reluctance by many people in the Middle East to believe that camels carry the virus and can make them sick," he says.

But camels aren't likely the only spreaders of MERS. People transmit the virus, too — and that may be a much bigger problem.

"There's increasing evidence of human-to-human transmission," Lipkin tells Shots. "Yes, we've demonstrated that camels can infect people. But the major challenge facing us now is to stop human-to-human transmission of MERS."